The overall objective of this project is an increased understanding of immunorecognition and the basis of allogeneic incompatibilities, especially from a phylogenetic perspective. Existence of a highly discriminating alloimmune reaction has been demonstrated in representative species of reef and soft corals. Although immune reactivity in thee "lower" animals is surprisingly similar to that found in mammals, the underlying mechanisms have not been discovered and are currently controversial. While the human immune system is exceedingly complex and involves interactions of numerous cells and factors, basic findings in these simpler animals could provide important insights in understanding more elaborate immunologic mechanisms. Proposed studies will focus on the following questions in Swiftia exserta, a gorgonian coral: 1. Further characterization of immunocytes and their function. Histochemistry and electron microscopy will be used to examine tissues under the experimental conditions of wound healing and allografting to determine the structure/function relationships of the cells as well as testing the capability of specific cells with regards to phagocytosis, adherence and agglutination. 2. Mechanisms of cytotoxicity. Cytotoxicity will be examined through in vitro and in vivo experiments to (a) test the specificity of the cytotoxic response, (b) identify the cytotoxic cell and test the hypothesis of a soluble cytotoxic factor, (c) test the hypothesis that apoptosis is involved in allograft rejection, and (d) start isolating the genes involved in the allograft rejection. 3. Immunological Memory. Experiment will demonstrate the duration of alloimmune memory, test for the persistence of allogeneic cells as a stimulus and examine the effects of temperature on memory. 4. Cellular aspects of alloimmunity. A series of experiments will examine cellular recognition, activation, movements and regulation involved in the alloimmune response. 5. Genetics of histocompatibility. A large series of allografts will be made in conjunction with microsatellite based DNA fingerprinting to test the hypothesis that the underlying genetics of Swiftia histocompatibility fits Medawar's concept of the "Uniqueness of the Individual."